This invention relates to frequency and amplitude demodulation systems which provide either frequency demodulation or amplitude demodulation or both with respect to an applied reference signal.
Prior art frequency demodulation systems require that the reference frequency be provided by means of a tuned structure as in phase, slope and ratio detector circuits; or, by means of a voltage controlled reference oscillator as in a phase locked loop. This invention provides detection about an applied reference signal frequency, eliminating the need for a tuned structure, and does not require phase, frequency or other synchronous locking to obtain frequency demodulation. This invention provides a novel and useful feature of producing an instantaneous replica of the frequency difference of two applied signal frequencies, and that the output may be linear.